Highly wear-resistant zinc base alloy



drawing and forming operations.

United States Patent HIGHLY WEAR-RESISTANT ZINC BASE ALLOY James C. Holzwarth, Royal Oak, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware No Drawing. Application August 8, 1950, Serial No. 178,345 9 Claims. (Cl. 75-178) This invention relates to. an improved zinc base alloy and a process for producing such an alloy. More particularly the invention relates to an alloy of this type which is characterized by' outstanding wear resistance properties due to the addition of an alloy hardener containingnickel and titanium.

Zinc base alloys commerciallyused today for purposes such as drawing dies usually possess inadequate wear properties for many requirements. It is therefore a prin cipal object of thepresent invention to overcome this inadequacy by providing a zinc base alloy characterized by greatly increased Wearproperties, high resistance to fracture, good castability and homogeneity. These desirable characteristics are obtained in a zinc base alloy by the addition of nickel and titanium to form wear-resistant particles of optimum size and distribution. In particular, I have found that a zinc base. alloy which contains aluminum and copper and preferably also magnesium is especially benefited with respect to its wear resistance properties by the addition of nickel and titanium.

It is a further object of this invention to provide an inexpensive zinc base alloy possessing a low melting point and uniform shrinkage. The low melting point eliminates the need for elaborate equipment in the alloying procedure, only a comparatively simple gasor oil-fired melting kettle being required. The uniform shrinkage characteristic permits the exact size of castings to be predetermined with precision, eliminating the necessity for extensive use of profiling machines. Accordingly, this alloy is ideally suited for use as drawing dies inasmuch as the entire processing of dies composed of this alloy is comparatively simple, requiring a minimum of equipment and labor. Cost is further reduced by the fact that this alloy can be remelted many times, permitting the alloy in obso lete dies to be almost entirely recovered. r In addition, the facility with which this alloy can be cast and the diversity of forms into which the molten alloy will flow make it a very desirable material for a variety of purposes. Furthermore, castings of this zinc base alloy cool comparatively quickly, making them available for production within a relatively short time.

As hereinbefore indicated, such a long-wearing, ho-

mogeneous alloy having good castability properties provides an outstanding material for dies. Therefore, the provision of a drawing die of a zinc base alloy modified with nickel and titanium, and a process for alloying the same, are further purposes of this invention.

In accordance with the invention, the foregoing and other objects are attained to a particularly high degree in a zinc base alloy containing aluminum, copper, and magnesium by the addition thereto of small amounts of nickel and titanium. In this type of zinc base alloy the aluminum and copper are added to increase the tensile strength while magnesium is included to overcome the corrosive influences of any impurities which may remain.

The high resistance to wear obtained is due to the presence of hard particles formed. of nickel and titanium and which are believed to be the intermetallic compound NiaTi. Regardless of the chemical composition of the particles, their presence in the softer matrix material is responsible for the marked increase in wear resistance, particularly thetype of Wear experienced with dies in Furthermore, these hard particles, which closely approximate the specific "ice gravity of the zinc-rich melt, do not float so readily as do hardening particles formed by the addition of many other hardening agents. Hence the present invention provides an alloy which has proper particle distribution as Well as optimum particle size, resulting in physical characteristics which satisfy all requirements for an outstanding tool alloy.

Commercially satisfactory results were obtained in accordance with my invention with an alloy containing 2.0% to 5.0% aluminum, 0.5% to 5.0% copper, 0.16% to 3.0% nickel, 0.04% to 0.8% titanium, and the balance substantially all zinc. Moreover, the further addition to this alloy of 0.03% to 0.40% magnesium is beneficial to reduce the corrosive tendencies of impurities such as lead, cadmium, and tin. It will be understood, of course, that these alloys may also contain as other incidental impurities such elements as iron and silicon.

More specifically, I have obtained outstanding wear characteristics in a casting alloy comprising 3.0% to 5.0% aluminum, 2.0% to3.5% copper, 0.10% to 0.30% magnesium, 1.0% to 2.5% nickel, 0.2% to 0.6% titanium and 88.0% to 93.0% zinc. For obtaining optimum castability and wear resistance properties, I prefer an alloy consisting, by weight, of approximately 4.0% aluminum, 0.25% magnesium, 3.25% copper, 1.6% nickel, 0.5% titanium, and the balance zinc, except for incidental impurities.

Wear resistance, of course, is a function of both the size and distribution of the hard nickel-titanium particles. Since particle size and distribution are dependent on metal viscosity, solidification rate and methods of alloying, this invention also provides a preferred procedure for preparing the alloys to produce maximum wear resistance with minimum attrition. Although the desired compositions may be obtained by separately adding the nickel and titanium to the zinc-rich melt, I have found superior results are obtained by introducing these elements in the form of a copper-nickel-titanium alloy hardener. The hard constituent of nickel and titanium is believed to be formed in this hardener during its preparation. Therefore, in order to form long-wearing particles of suitable size, this hardener is preferably'added to the zinc as a solid alloy, the copper-rich phase surrounding this constituent being subsequently dissolved away by the zinc, leaving the harder nickel-titanium particles suspended in the zinc alloy.

The desired alloy composition is preferably obtained by melting substantially pure zinc and, after elevating the temperature of molten Zinc to a range between 950 F. and 1050 F., dissolving therein approximately 50% of the aluminum to be added. This latter step inhibits drossing of the zinc at higher temperatures. After further raising the temperature of the melt to approximately 1100 F. to 1300 F., the required amounts of copper, nickel and titanium are added, preferably in the form of a ternary hardening alloy in the solid state, as hereinbefore indicated. The elevated temperature should be maintained until the aforementioned copper-rich phase in this hardening alloy is entirely dissolved, the solution rate being increased by periodic agitation. After this solution is accomplished, I have found it desirable to lower the temperature of the melt to approximately 900 F. to 950 F. and to add the remaining 50% of the aluminum, the addition of which may be sutficiently early to aid in this cooling process. A suitable flux, such as ammonium chloride, may then be added to remove any objectionable oxides, after which the magnesium is introduced by preferably submerging it in the bath. The final alloy may be then cast to shape in suitable molds.

Although the aluminum could alternatively all be added either before or after the addition of the coppernickel-titanium hardener, the above alloying sequence has been found to be most satisfactory. r

In accordance with my invention, satisfactory results have been provided with a copper-nickel-titanium hardener having the following composition: 45% to 90% copper, 8.0% to 40% nickel, and 2.0% to 15% titanium. However, to obtain optimum particle size I prefer to use a hardener which consists of 55% to 70% copper, 20% to 35% nickel and 4.0% to titanium.

It is to be noted that in these alloy compositions the ratio of nickel to titanium corresponds approximately to the inter-metallic compound NiaTi. Therefore, for optimum homogeneity and wear properties the titanium content should thus be held within the range of approximately to 30% of the combined weight of nickel and titanium, 22% being the percentage which appears to produce the most outstanding results. Accordingly, the hardening alloy which I found to be most satisfactory consisted of approximately 62% copper, 30% nickel and 8% titanium. These hardeners, when added to the zinc-rich melt in the proportions hereinbefore indicated, form NizTi particles which preferably comprise 1.0% to 3.1 of the zinc base alloy.

Inasmuch as the hard particles of nickel and titanium are formed in the alloy hardener during its preparation, the alloying procedure of this hardener is of considerable importance in achieving optimum results. Melting of the hardener should be carried on under an atmosphere of a suitable inert gas, such as argon, to reduce the normal small loss of titanium due to oxidation. I have obtained most satisfactory melting and high titanium recovery using an induction furnace under an argon gas atmosphere.

Accordingly, this copper-nickel-titanium hardening alloy is preferably prepared by melting the copper and adding electrolytic nickel thereto. The alloy is subsequently preferably heated to a temperature between 2500 F. and 3000 F. and the melt blanketed with the argon atmosphere, the titanium then being added to the melt either as commercial nickel-titanium or commercially pure titanium. In the former case, of course, the initial addition of the nickel would have to be reduced accordingly to provide for the proper final nickel content. These additions are preferably made slowly to permit proper solution and to keep the melt from chilling excessively before casting, the casting temperature preferably being in the range of approximately 3000 F. to 3200 F. Inasmuch as it is desirable to cast the metal in shapes which will dissolve most readily in the molten zinc-rich alloy, I prefer to form castings having a high ratio of surface area to volume, such as flat plates or thin sheets.

Although the present alloy has been described as particularly suitable as a drawing die material, it may also be employed to considerable advantage in other applications wherein high wear resistance, good castability and homogeneity are of importance.

While I have set forth herein specific examples of zinc base alloys possessing high Wear resistance characterists due to the addition of nickel and titanium, it is not intended to restrict the invention to any specific zinc base alloy. I believe that I am the first to have discovered the value of adding nickel and titanium to zinc base alloys generally, and it is therefore desired to cover such discovery in broad terms.

I claim:

1. A zinc base alloy consisting essentially of approximately 2% to 5% aluminum, 0.5% to 5% copper, 0.16% to 3% nickel, 0.04% to 0.8% titanium and the balance zinc plus incidental impurities, a substantial portion of said nickel and titanium being present in the form of dispersed hard particles of nickel-titanium.

2. A highly wear-resistant zinc base alloy consisting essentially of approximately 2% to 5% aluminum, 0.5 to 5% copper, 0.03% to 0.4% magnesium, 0.16% to 3% nickel, 0.04% to 0.8% titanium and the balance zinc plus incidental impurities, a substantial portion of said nickel and titanium being present in the form of dispersed hard particles of an intermetallic compound of nickel and titanium.

3. An alloy consisting essentially of 3.0% to 5.0% aluminum, 2.0% to 3.5% copper, 0.10% to 0.30% magnesium, 1.0% to 2.5% nickel, 0.2% to 0.6% titanium and 88% to 93% zinc, a substantial proportion of said nickel and titanium being present in the form of hard particles of nickel-titanium.

4. A casting alloy consisting essentially of 3.0% to 5.0% aluminum, 2.0% to 3.5% copper, 0.10% to 0.30% magnesium, approximately 1% to 3.1% hard nickeltitanium particles and the balance zinc and incidental impurities.

5. A process of forming a wear-resistant zinc base casting alloy which consists of melting commercially pure zinc and dissolving therein a quantity of aluminum equal to 2% to 5% of the final alloy and an alloy hardener consisting of copper, nickel and titanium, the composition of said hardener being such that the final alloy contains 0.5 to 5% copper, 0.16% to 3% nickel and 0.04% to 0.8% titanium, said hardener being added at a temperature between 1100 F. and 1300 F., fluxing the melt to remove objectional oxides, and subsequently dissolving in the melt an amount of magnesium equal to 0.03% to 0.4% of the final alloy.

6. A highly wear-resistant zinc base alloy consisting essentially of 88% to 93% zinc, 2% to 5% aluminum, 0.5% to 5% copper, and approximately 1% to 3.1% dispersed hard particles of a nickel-titanium intermetallic compound, the titanium content in said compound constituting about 15 to 30% of the combined weight of nickel and titanium.

7. A highly wear-resistant zinc base alloy consisting essentially of 2% to 5% aluminum, 0.5 to 5% copper, 0.16% to 3% nickel, 0.04% to 0.8% titanium and the balance zinc plus incidental impurities, a substantial portion of said nickel and titanium being present in the form of dispersed hard particles of NiaTi, the titanium content of said alloy constituting approximately 15 to 30% of the combined weight of nickel and titanium.

8. A zinc base alloy characterized by high wear resistance consisting essentially of 2% to 5% aluminum, 0.5% to 5% copper, 1% to 2.5% nickel, 0.2% to 0.6% titanium and the balance substantially all zinc, a substantial portion of said nickel and titanium being present in the form of hard particles of nickeltitanium.

9. A casting alloy characterized by high wear resistance consisting essentially of 2% to 5% aluminum, 0.5% to 5% copper, 0.03% to 0.4% magnesium, 1% to 2.5% nickel, 0.2% to 0.6% titanium and the balance zinc plus incidental impurities, a substantial portion of said nickel and titanium being present in the form of dispersed hard particles of NiaTi, the titanium content of said alloy constituting approximately 15 to 30% of the combined weight of nickel and titanium.

References Cited in the file of this patent UNITED STATES PATENTS 1,364,654 Tedesco Jan. 4, 1921 1,540,006 Hodson June 2, 1925 2,013,870 Starmann Sept. 10, 1935 2,137,281 Hensel et al Nov. 22, 1938 2,222,157 Ruzicka Nov. 19, 1940 2,317,179 Daesen Apr. 20, 1943 2,357,190 Evans Aug. 29, 1944 FOREIGN PATENTS 182,122 Great Britain May 24, 1923 336,881 Great Britain Oct. 23, 1930 362,507 Great Britain Dec. 7, 1931 420,672 Great Britain Aug. 18, 1933 OTHER REFERENCES Iron Age, August 3, 1944, pages 46-49, 132, 134. 

1. A ZINC BASE ALLOY CONSISTING ESSENTIALLY OF APPROXIMATELY 2% TO 5% ALUMINUM. 0.5% TO 5% COPPER, 0.16% TO 3% NICKEL. 0.04% TO 0.8% TITANIUM AND THE BALANCE ZINC PLUS INCIDENTAL IMPURITIES. A SUBSTANTIAL PORTION OF SAID NICKEL AND TITANIUM BEING PRESENT IN THE FORM OF DISPERSED HARD PARTICLES OF NICKEL-TITANIUM. 